This invention relates to a method of cleaning an ion source, and/or to a corresponding apparatus/system. In certain example embodiments, both the anode and cathode of the ion source are negatively biased during at least part of a cleaning mode in order to clean the ion source.
An ion source is a device that causes gas molecules to be ionized and then accelerates and emits the ionized gas molecules and/or atoms in a beam toward a substrate. Such an ion beam may be used for various purposes, including but not limited to cleaning a substrate, activation, polishing, etching, and/or deposition of thin film coatings/layer(s). Example ion sources are disclosed, for example, in U.S. Pat. Nos. 6,359,388; 6,037,717; 6,002,208; and 5,656,819, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2 illustrate a conventional ion source. In particular, FIG. 1 is a side cross-sectional view of an ion beam source with an ion beam emitting slit defined in the cathode, and FIG. 2 is a corresponding sectional plan view along section line IIxe2x80x94II of FIG. 1. FIG. 3 is a sectional plan view similar to FIG. 2, for purposes of illustrating that the FIG. 1 ion beam source may have an oval and/or racetrack-shaped ion beam emitting slit as opposed to a circular ion beam emitting slit. Any other suitable shape may also be used.
Referring to FIGS. 1-3, the ion source includes a hollow housing made of a magnetoconductive material such as steel, which is used as a cathode 5. Cathode 5 includes cylindrical or oval side wall 7, a closed or partially closed bottom wall 9, and an approximately flat top wall 11 in which a circular or oval ion emitting slit and/or aperture 15 is defined. The bottom 9 and side wall(s) 7 of the cathode are optional. Ion emitting slit/aperture 15 includes an inner periphery as well as an outer periphery.
Deposit and/or maintenance gas supply aperture or hole(s) 21 is/are formed in bottom wall 9. Flat top wall 11 functions as an accelerating electrode. A magnetic system including a cylindrical permanent magnet 23 with poles N and S of opposite polarity is placed inside the housing between bottom wall 9 and top wall 11. The N-pole faces flat top wall 11, while the S-pole faces bottom wall 9. The purpose of the magnetic system with a closed magnetic circuit formed by the magnet 23 and cathode 5 is to induce a substantially transverse magnetic field (MF) in an area proximate ion emitting slit 15. The ion source may be entirely or partially within wall 50. In certain instances, wall 50 may entirely surround the source and substrate 45, while in other instances the wall 50 may only partially surround the ion source and/or substrate.
A circular or oval shaped conductive anode 25, electrically connected to the positive pole of electric power source 29, is arranged so as to at least partially surround magnet 23 and be approximately concentric therewith. Anode 25 may be fixed inside the housing by way of insulative ring 31 (e.g., of ceramic). Anode 25 defines a central opening therein in which magnet 23 is located. The negative pole of electric power source 29 is connected to cathode 5, so that the cathode is negative with respect to the anode.
Generally speaking, the anode 25 is generally biased positive by several thousand volts. Meanwhile, the cathode (the term xe2x80x9ccathodexe2x80x9d as used herein includes the inner and/or outer portions thereof) is generally held at, or close to, ground potential. This is the case during all aspects of source operation, including during a mode in which the source is being cleaned.
The conventional ion beam source of FIGS. 1-3 is intended for the formation of a unilaterally directed tubular ion beam, flowing in the direction toward substrate 45. Substrate 45 may or may not be biased in different instances. The ion beam emitted from the area of slit/aperture 15 is in the form of a circle in the FIG. 2 embodiment and in the form of an oval (e.g., race-track) in the FIG. 3 embodiment.
The conventional ion beam source of FIGS. 1-3 operates as follows in a depositing mode when it is desired to ion beam deposit a layer(s) on substrate 45. A vacuum chamber in which the substrate 45 and slit/aperture 15 are located is evacuated, and a depositing gas (e.g., a hydrocarbon gas such as acetylene, or the like) is fed into the interior of the source via aperture(s) 21 or in any other suitable manner. A maintenance gas (e.g., argon) may also be fed into the source in certain instances, along with the depositing gas. Power supply 29 is activated and an electric field is generated between anode 25 and cathode 5, which accelerates electrons to high energy. Anode 25 is positively biased by several thousand volts, and cathode 5 is at ground potential or proximate thereto as shown in FIG. 1. Electron collisions with the gas in or proximate aperture/slit 15 leads to ionization and a plasma is generated. xe2x80x9cPlasmaxe2x80x9d herein means a cloud of gas including ions of a material to be accelerated toward substrate 45. The plasma expands and fills (or at least partially fills) a region including slit/aperture 15. An electric field is produced in slit 15, oriented in the direction substantially perpendicular to the transverse magnetic field, which causes the ions to propagate toward substrate 45. Electrons in the ion acceleration space in and/or proximate slit/aperture 15 are propelled by the known E x B drift in a closed loop path within the region of crossed electric and magnetic field lines proximate slit/aperture 15. These circulating electrons contribute to ionization of the gas (the term xe2x80x9cgasxe2x80x9d as used herein means at least one gas), so that the zone of ionizing collisions extends beyond the electrical gap between the anode and cathode and includes the region proximate slit/aperture 15 on one and/or both sides of the cathode 5.
For purposes of example, consider the situation where a silane and/or acetylene (C2H2) depositing gas is/are utilized by the ion source of FIGS. 1-3 in a depositing mode. The silane and/or acetylene depositing gas passes through the gap between anode 25 and cathode 5. Unfortunately, certain of the elements in acetylene and/or silane gas is/are insulative in nature (e.g., carbide may be an insulator in certain applications). Insulating deposits (e.g., carbide deposits, carbon deposits, and/or oxide deposits which may be insulating or semi-insulating in nature) resulting from the depositing gas can quickly build up on the respective surfaces of anode 25 and/or cathode 5 proximate the gap therebetween, and/or at other electrode locations. This can interfere with gas flow through the gap and/or aperture 15, and/or it can reduce net current thereby adversely affecting the electric field potential between the anode and cathode proximate slit/aperture 15. Such deposits resistively limit the amount of current that can flow through the source; this adversely interferes with the operability and/or efficiency of the ion source especially over significant lengths of time. This unfortunately can also result in micro-particles from the deposits making their way into a film being deposited on the substrate. In either case, operability and/or efficiency of the ion beam source is adversely affected.
These undesirable build-ups eventually have to be cleaned off the anode and/or cathode. Conventionally, cleaning has been conducted by running the source as shown in FIG. 1 while introducing oxygen gas into the source. Unfortunately, this type of ion source cleaning technique does not do an adequate job of cleaning the anode, and anode/cathode surfaces distant from the aperture 15 tend not to be cleaned very well.
In view of the above, it will be apparent to those skilled in the art that there exists a need for a more efficient technique for cleaning an ion source.
In certain example embodiments of this invention, both the anode and cathode of the ion source are negatively biased in order to clean the same. Surprisingly, it has been found that when the anode and cathode of an ion source are both negatively biased, undesirable build-ups (e.g., carbon inclusive build-ups) on surface(s) of the anode and/or cathode are more easily and/or quickly removed during cleaning.
In certain example embodiments of this invention, oxygen inclusive gas may be provided in the ion source during cleaning mode(s). In such embodiments, generated oxygen ions are accelerated or otherwise directed toward the anode and/or cathode in order to help remove residue (e.g., carbon inclusive build-ups) from the surface(s) thereof. In certain embodiments, the removal of carbon inclusive build-ups may be accelerated by chemical oxidation of the carbon, and/or may be caused by physical ablation of the build-ups by the accelerated ions. Gas other than oxygen may be used for cleaning in other embodiments.
In certain example embodiments of this invention, there is provided a method of cleaning an ion source, the method comprising: providing the ion source which includes an anode and a cathode; and negatively biasing both the anode and cathode during at least part of a cleaning mode.
In certain other example embodiments of this invention, there is provided a method of cleaning an ion source, the method comprising: providing the ion source including an anode, a cathode, and a magnet, wherein at least one of the anode and the cathode includes an ion emitting aperture defined therein that is used for directing ions toward a substrate during a depositing mode of operation of the ion source; and during at least part of a cleaning mode, negatively biasing both the anode and the cathode of the ion source while at least one gas for ionization is present proximate the anode and/or cathode, so that the anode and/or cathode can be cleaned.
In certain other example embodiments of this invention, there is provided an ion source comprising: an anode; a cathode; wherein at least one of the anode and cathode comprises an ion emitting aperture defined therein; and means for negatively biasing the anode and cathode during at least part of a cleaning mode so that the anode and/or cathode can be cleaned during the cleaning mode. In certain example embodiments, the anode is positively biased with respect to the cathode during a depositing mode of source operation (i.e., when the ion source is being used to ion beam depositing a layer(s) on a substrate); and the anode and cathode are both negatively biased during the cleaning mode.
In certain other example embodiments of this invention, there is provided a method of cleaning an ion source, the method comprising: providing the ion source which includes an anode and a cathode, wherein at least one of the anode and cathode includes an ion emitting aperture defined therein; during a cleaning mode, biasing the anode and cathode so that the anode and/or cathode can be cleaned by sputtering undesirable build-ups off of respective surface(s) of the anode and/or cathode; and determining when to stop the sputtering in the cleaning mode based upon at least a change in sputtering voltage present during the cleaning mode due to the biasing.